The invention relates to devices for driving current through inductive elements, and in particular, to devices that drive current through write heads that write to magnetic storage media.
Magnetic storage media, which include magnetic tape and magnetic disks, are used for storage and retrieval of data. Data may be read from or written to a magnetic medium with a read/write head assembly, which includes one or more transducer heads. The data are encoded in magnetizations on the recording surface.
The data stored on the magnetic medium are usually organized into xe2x80x9cdata tracks,xe2x80x9d and the transducer heads write data to and/or read data from the data tracks. A typical magnetic storage medium includes several data tracks.
As the number of data tracks on a medium increases, the data storage capacity of the medium increases. The data tracks also usually become narrower, as more data tracks are crowded onto the recording surface of the medium.
For proper data storage and recovery, a transducer head must locate each track where data are to be written or read, and follow the path of the data track accurately along the surface of the medium. A servo control system typically is provided to control the positioning of the head relative to the data tracks.
One technique used to position the head relies upon servo position information at pre-selected sites on the medium. This servo position information, which is usually recorded during the medium manufacturing process, is then used by the servo control system to control head motion when seeking between tracks, and to regulate head position on a track during reading and/or writing.
One format for storing servo position information is a time-based format. Unlike a conventional servo track format, which stores servo data as magnetic flux transitions of varying phases or frequencies, time-based servo marks store servo data in a series of patterns of marks. Typical patterns include a diamond or zigzag. Time-based servo marks are usually of a very short duration, and consequently consume less space on the recording surface than servo tracks.
Because time-based servo marks are of a very short duration, the marks usually are recorded with an intense magnetic pulse that is quickly generated and quickly dissipated. The present invention provides techniques for generating an intense magnetic pulse very quickly. The present invention includes a device that drives a pulse of high current through a write head, which generates a burst of magnetic flux that in turn generates a high-intensity fringing field. The high-intensity fringing field may be used to write time-based servo marks on a magnetic medium.
The inductance of the write head prevents instantaneous high current flow through the write head. To rapidly build up the current through the write head, the write head is coupled to a high voltage source. A switching circuit holds both terminals of the write head at the high voltage supplied by the high voltage source, preventing current from flowing in the write head. In response to a signal from a control circuit, the switching circuit provides a path for current to flow through the write head. As a result, the voltage at one of the terminals of the write head rapidly drops. Current flow through the write head rises rapidly, which causes a burst of magnetic flux and generates a high-intensity magnetic fringing field.
The current pulse is usually of short duration. In response to a signal from a control circuit, the switching circuit opens the current path, preventing current from flowing through the switching circuit. The current flowing in the write head, no longer having a path through the switching circuit, dissipates in dissipating circuit elements. The current in the write head and the magnetic flux drop rapidly.
In one embodiment, the invention presents a device comprising a write head and a switching circuit. When the switching circuit is in a conducting state, current is allowed to flow through the write head. When the switching circuit is in a non-conducting state, current ordinarily does not flow through the write head. The device may include a high-voltage dc source coupled to the write head and a control circuit that regulates the states of the switching circuit.
In another embodiment, the invention presents a method comprising supplying a high voltage to a first terminal of a write head and holding a second terminal of the write head at the high voltage. While the second terminal is held at the high voltage, no current flows through the write head. The method further comprises dropping the voltage at the second terminal of the write head to cause current to flow through the write head. Because of the inductance of the write head, the current in the write head cannot cease flowing immediately. Accordingly, the method also includes dissipating the current with a dissipative element such as a resistor.
In a further embodiment, the invention presents a method comprising generating a controlling pulse, and opening and closing a switch as a function of the controlling pulse. The method further comprises driving current through a write head when the switch is closed and dissipating the current with a dissipative element when the switch is open.
In an additional embodiment, the invention comprises a device that includes a voltage source, a write head, a damping resistor in parallel with the write head, a dissipating resistor, a diode, a switching circuit and a control circuit that generates a control signal. The switching circuit is in either a conducting state or a non-conducting state as a function of the control signal. When the switching circuit is in a conducting state, current flows through the write head.
The details of one or more embodiments of the present invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the present invention will be apparent from the description and drawings, and from the claims.